Enter now accepts the highlighted item like Tab whenever the popup is
open; dismiss with Escape first to insert a plain newline. Drops the
`engaged` gate that only accepted after navigating the menu.
Anchoring the popup below the caret let it spill off the right/bottom of
the window when the caret sat at the edge, so the browser clipped it.
After render, measure the popup and shift it left off the right edge or
flip it above the caret line when there's no room below.
Enter kept hijacking the auto-opened popup mid-typing. Now Tab always
accepts, while Enter accepts only once the author has moved the selection
(arrow / Ctrl-N/P); an untouched popup lets Enter insert a newline.
A fractional line box (0.8rem × 1.6) is rounded differently by the
textarea than by the <pre> backdrop, so the caret drifted further from
its glyph the lower it sat — worst at the bottom of a tall file.
Accepting an enum value (e.g. "on-track") re-ran the chained refresh,
which re-matched the value and reopened the popup. Chain only after
completing a key, when there are still values to offer.
Anchor a suggestion list at the caret (monospace metrics, re-anchored on
scroll), with arrow/Enter/Tab/Esc handling and click-to-accept. Accepting
a key like `status` chains straight into its value suggestions.
